Wide-range muffle type oven furnace



J y 1954 .1. WALLERIUS EIAL WIDE-RANGE MUFFLE TYPE OVEN FURNACE 3 Sheets-Sheet 1 y 1954 J. WALLERIUS ETAL 2,683,595

WIDE-RANGE MUFFLE TYPE OVEN FURNACE Filed Aug. 24, 1949 5 Sheets- Sheet 2 y 1954 J. WALLERIUS ETAL 2,683,595

WIDE-RANGE MUFFLE TYPE OVEN FURNACE Filed Aug. 24, 1949 3 Sheets-Sheet a Patented July 13, 1954 UNITED ATENT OFFICE E-RAN GE MUFFLE TYPE OVEN FURNACE Application August 24, 1949, Serial No. 112,061

1 Claim.

This invention relates to furnaces and more particularly to small mufiie furnaces of the gas fired type.

Although annealing, normalizing, carburizing, forging, and miscellaneous heat treating operations are done to some extent in most shops, the major heat treating operation is the hardening of carbon steels. Ordinarily this consists of three operations: hardening, quenching, and tempering. In general to harden steel, it is first heated to a temperature approximately 25 to 75 degrees Fahrenheit above its critical range (approximately 1450 degrees to 1650 degrees Fahrenheit for carbon steels, and 1800 degrees to 2&00 degrees Fahrenheit for the higher alloy and high speed steels). After being heated to this temperature the steel is quenched or cooled rapidly in oil, water, brine, air or similar cooling medium. The tempering operation consists of reheating the steel after the hardening and quenching steps to a temperature below the lower limit of the critical range. This relieves hardening strains and stresses and effects desired physical properties in the steel. The quenching and tempering steps should follow as soon as possible after the hardening process. Thus for ordinary steels, heretofore two furnaces have been required for treating them; one furnace having an operating temperature between 1400 degrees and 1800 degrees Fahrenheit for heating the steel 9 in the hardening step, and a second furnace having a temperature between 300 degrees and 800 degrees Fahrenheit for heating the steel after it is quenched to temper it.

In the case of high speed alloy steels, the correct hardening temperature is from 1800 degrees to 2400 degrees Fahrenheit. Because there is a likelihood of cracking or damaging the work if it is placed directly in a furnace at this high temperature it is necessary to pre-heat the work in furnaces having an operating temperature between 1400 degrees and 1600 degrees Fahrenheit. Since the steps of preheating, hardening, quenching and tempering are all done practically simultaneously, it is necessary therefore in the handling of high speed and high alloy steels to provide three furnaces; one for the preheating operation having an operating temperature between 1400 degrees and 1600 degrees Fahrenheit, one for the hardening operation having an operating temperature between 1800 degrees and 2400 degrees Fahrenheit, and one for the tempering operation having an operating temperature between approximately 400- degrees and 1200 degrees Fahrenheit.

From the above it will be seen that the temperature range in the heat treating of steels varies from approximately 300 degrees to 2400 degrees Fahrenheit. Heretofore gas fired furnaces have not been satisfactory for operation throughout this temperature range. Accordingly as stated above, separate furnaces have been required for different temperature ranges depending upon the particular step of the heat treating process involved. Because two and three furnaces are usually required in the heat treating of steels, a smaller manufacturer is somewhat handicapped by the fact that a plurality of furnaces take up a considerable amount of space in his factory and require the investment of a considerable amount of capital. Accordingly many small manufacturers have not had installations whereby they could satisfactorily heat treat steels, particularly high alloy steels.

An object of the invention is the provision of a novel gas fired furnace of the above character that is capable of operating throughout the temperature range required for pre-heating, hardening and tempering carbon and high alloy steels.

Another object of the invention is the provision of a furnace of the above character having means for readily converting the furnace from a semimuflle to a muffle furnace.

Another object of the invention is the provision of a furnace of the above character having novel burners for supplying heat to the furnace.

Another object of the invention is the provision of a furnace of the above character having novel means for igniting the burners.

Another object of the invention is the provision of a furnace of the above character whereby the atmosphere can be changed from a reducing to an oxidizing atmosphere.

Another object of the invention is the provision of a furnace of the above character which can be rapidly changed from one temperature to another temperature throughout its range of operation.

Another object of the invention is provision of a furnace operable over an extremely wide range of temperatures that can be set to operate at any intermediate temperature.

Another object of the invention is the provision of a furnace of the above character where in heat treating processes formerly requiring a plurality of furnaces can be effected in a single furnace.

Another object of the invention is the provision of a furnace of the above character that is simple in construction, that is highly effective for the purpose intended, that is rugged and that is relatively inexpensive to produce.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which- Figure l is a front elevational view of a furnace embodying the present invention with a portion cutaway to show details of construction;

Fig. 2 is a sectional view of the furnace taken along the section line 22 of Figure 1;

Fig. 3 is a plan view of the furnace shown in Figure 1;

Fig. 4 is a sectional view taken substantially along the line 64 of Fig. 3;

Fig. 5 is an enlarged. fragmentary sectional view of the furnace through one of the burners showing the details of construction, and

Fig. 6 is a sectional view taken substantially along the line 56 of Fig. 5..

Referring now to the drawings, the invention is shown embodied. in a small furnace comprising a generally circular heating chamber .3 i, an oven unit for containing a workpiece i3 disposed in the chamber l i and at least one burner i l on each side of the chamber ll disposed below the oven unit and mounted so that the products of combustion and the heat from the burner are directed into the chamber H .in a manner to be directed against the wall on the opposite side of the chamber so as to swirl about the oven unit.

As best seen in Figs. 2 and 4 the chamber 5 l is defined by a horizontal sleeve It, the walls of which are formed by .arcuate sections i? interconnected by tongue and groove joints l5. opposite ends of the sleeve 1.6 are disc shaped end portions 19 and 2!. Each of the end portions I9 and 2| is formed with an annular groove 22 shaped to receive an annular tongue 23 formed on the axial faces of the sleeve IS. The sections 1'! and end portions I'El and 2| may be formed from any suitable refractory material. A sleeve of insulating material '24 envelopes the periphcries of the end portions 19 and 2| and the sleeve portion l6 and a suitable sheathing of steel 25 surrounds the insulating material 2&. At the rear end of the furnace the disc 2| is covered with a layer of insulating material 21. A steel end cap 28 formed with an annular flange 25 shaped to telescope over the rear end of the sheathing 26 forms a cover for the rear end of the furnace and maintains the layer of insulating material 21 in side by side relation with the 2!. The forward end portion 19 is formed with an opening 32 defined by a flat bottom portion and an arched top portion shaped to receive and. support a sleeve portion 33 having an opening 34 of conventional configuration for placing articles in and removing them from the chamber H. The sleeve 33 projects beyond the outer face of the end portion l9 and is supported at its outer end by a support member SI of refractory material in side-by-side relation with the .bottom portion of the end portion IS. The outer axial face of the sleeve 33 is disposed in a plane inclined with respect to the vertical axis of the furnace as shown in Fig. 2 to provide a mounting for a door 36 as disclosed in Patent No. 2,279,484, issued January 20, 1942. A layer of insulating material 37 is disposed in side-by-side relation with the member 3i and the top portion of the end 19. A cap 33 having a flange portion 39 shaped to telescope over the forward end of the sheathing 25 forms a cover for the front of the furnace and maintains the layer of insulating material 31 in its assembled relation. Suitable tie rods extend between the caps 28 and iiandv secure the component parts of the furnace in their assembled relation. The furnace may be mounted on any suitable stand 32, a portion only of the latter being shown herein.

The door 35 normally covers the opening 34 and is arranged to be moved vertically to uncover the opening 3% to permit access to the chamber ll. For this purpose the top of the door is connected to cables trained over spaced pulleys M supported on a shaft 4E at the forward end of the furnace. The latter is supported by spaced brackets 47 mounted on the top of the furnace as shown in Figs. 1 and 3. One end of the shaft 36 is formed as a crank so. At the rear end of the furnace the cables 63 pass over spaced sheaves 53 mounted on a shaft 52 supported by the brackets ll. A weight 53 at the rear end of the furnace is connected to the cables 53 and provides a counterbalance for the door 3%. By rotating the crank ie in one direction the door may be raised and by rotating the crank in the opposite direction the door may be lowered.

One aspect of the invention is concerned with novel means disposed in the furnace whereby the furnace can be readily converted from a full muille furnace to a semi-muffle furnace. For this purpose, as best shown in Figs. 2 and 4, the oven unit is formed in two parts; the base part 5 1- and a cover part 56. The base part 54 in e'lfect defines a fiat hearth which is supported at the rear end of the chamber II by the lower side wall defining the recess 5? formed in the end portion '21 and at the front end of the chamber by the bottom wall defining the opening 32 in the end 19. The upper surface of the hearth is in alinemen't with the bottom fiat portion of the sleeve member 33 so that articles may be readily placed in or removed from the furnace. An upright '56 disposed between the bottom of the furnace and the hearth 511 forms a support for the central portion of the hearth 54. On its side edges the hearth is formed with upturned flanges 59 as best seen in Fig. l spaced inwardly from the sides of the chamber H. On their extreme upper surfaces the flanges are formed with axially extending grooves 61. The cover portion 56 is shaped to be removable through the openings 32 and 34 and comprises a generally inverted U-shapecl member (see Fig. 4) having a bridging portion 62 adapted to be in spaced relation with the hearth 5d and legs 63 spaced apart the distance between the flanges 59 on the hearth 54. On their extreme lower ends the legs 63 are formed with axially extending tongues 64 shaped to fit in the grooves 6| formed on the flanges 59. At the rear end of the chamber H the cover portion 56 is received in a groove 88 formed in the end 2!. At the opposite end of the chamber the cover portion 56 is disposed in the opening 32 formed in the end H3. The configuration of the cover portion 56 is such that when the tongues 8 1 fit in the grooves 6|, the outer walls of the cover portion fit snugly in side by side relation with the side walls defining the opening 32, yet permit the cover portion to be withdrawn from the chamber l l through the openings 32 and 34.

The burners it are mounted on the sides of the chamber l l as best shown in Figs. 3 and 5. Each of the burners Hi comprises a body ll having a central passage 75?, defined by an annular partition 73 formed in the body, and an annular chamber M surrounding the passageway E2. At

one end the passageway I2 is shaped to be connected to a gas conduit '16. At its opposite end the passageway is closed by a wall I! having a plurality of annularly spaced ports 18. Each of the ports is directed outwardly at an angle with respect to the longitudinal axis of the passageway l2. The annular passageway Ed is arranged to be in communication with an air conduit 9. At the end of the chamber T l adjacent the furnace the body ii is formed with a plurality of annularly arranged passageways 8! in concentric relation with the ports 78. The passageways 85 are directed inwardly toward an extension of the longitudinal axis of the passageway I2. The body i! is formed with a mounting flange 82 having slots 83 formed on opposite sides. The slots 823 are shaped to receive bolts 84 threadable into a boss 86 secured to the external sheathing 2'8 of the furnace. The ports I8 and 8! are arranged to be in communication with a horizontally extending passageway 81 formed in a sleeve member 83 received in the boss 83. The passageway 81 is in communication with a passageway 8% formed in the wall of the sleeve It. The passageway 83 opens into the chamber I I at a position below the hearth 5 2. As best shown in Fig. 4-, four burners M are employed in this construction. It is to be understood however that any desired number of burners may be used. The

burners are preferably disposed at staggered positions along opposite sides of the chamber I I.

Suitable means is provided for supplying gas and air to the respective burners It. To this end the conduit id for each burner id is connected to a vertical conduit 99 (see Figure 1) having a burner control valve 9! connected in series therewith. Each conduit 96 is connected to a horizontal conduit 92 (see Fig. 3). The latter are connected to a common vertical conduit 93 (Figure 1) in turn connected to a horizontal gas supply line as beneath the furnace. A main gas shut-off valve 95 is connected in the supply line 9 3 for controlling the flow of gas therethrough. The air conduit 9 for each burner I4 is connected to a horizontal conduit 91 (see Fig. 3). An air control valve Q8 is disposed in each conduit is for adjusting the flow of air to each burner I4. Each conduit 91 is in turn connected to a com mon horizontal conduit 99 connected to an air supply line Hit. is connected in the air supply line for controlling the flow of air therethrough.

Suitable provision is made for igniting the burners i i. For this purpose the body II of each burner is provided with a recess III accessible from the top of the body II and shaped to be in communication with the passageway 81 when the body ii is mounted on the side of the furnace. A cover H2 pivotally mounted at one end on the body i! by a screw I93 is arranged to be movable between a position in which access may be had to the recess HI and a position in which the cover rests on top of the boss 85 as shown in Fig. 5 to close the recess l i i. When the cover I I2 is moved about its pivot to open the recess the burner may be ignited through this recess. In some instances with the cover 5 12 open, air may also be supplied to the burners through the recess III, particularly under low turn-down operating conditions. A projection Ii 4 on the cover H2 may be provided to facilitate moving the cover between its open and closed positions.

To convert the furnace from a mufiie furnace to a semi-muffle furnace, it is only necessary to raise the door 36 to clear the opening 32 and A main air shut-off valve I02 then grasp the cover 56 and pull it axially through the openings 32 and 34. The tongue and groove fit on both sides of the cover 56 in effect providing skidways whereby the cover may be readily removed from the chamber II. The end wall mountings for the base and cover insure that when the cover 56 is disposed in the chamber II, as shown in Fig. 2, it is in sealed relation with respect to the chamber I I and that the products of combustion from the chamber II cannot get into the interior of the muflle. Where desired a suitable atmosphere may be introduced into the muffle through an opening I I 5 formed in the end 2! of the chamber. An opening H6 in the door 36 permits inspection of the interior of the oven.

The operation of the furnace is readily apparent from the foregoing but may be summarized as follows: The gas and air valves 9| and 98 are adjusted so that the proper fuel mixture flows from the body II into the passageway 37. The cover H2 is moved to uncover the recess III and the burner is lighted by a match or the like. Thereafter the air and gas valves are adjusted so that a fuel mixture results that gives a preselected temperature in the chamber H. Fig. 5 shows how the flame of the burner appears when the desired temperature in the chamber ii is relatively low. The air from the annular ports 8I is directed inwardly toward the axis of the passageway 81. This tends to cause the gas flame to have a conical shape with the base of the flame being adjacent the burner. The products of combustion and heat are directed into the furnace beneath the hearth lid and against the opposite side of the wall of the furnace. The products of combustion are thence directed upwardly around the hearth following the curvature of the inside of the walls of the chamber. Thus in effect the products of combustion and heat waves are caused to swirl about the hearth. As shown in Fig. 5 the flame projects only a short distance into the passage 81 from the end of the burner.

When a higher temperature is desired in the furnace the fuel mixture is made richer so that the flame extends into the chamber II and follows the curvature of the walls of the chamber in the manner described for the products of combustion when the flame is low. As shown in Fig. 4 when the fuel is adjusted for a high temperature in the chamber II the flames line the inside of the chamber I I and swirl about the interior of the chamber. The arrangement of the ports BI and I8 insures that the air and gas are thoroughly mixed, the intermixture taking place adjacent the end of the body H and in the passageway 81. Thus in effect this construction provides a 100 percent primary air burner. This construction permits of good flame control which is not true of constructions using pre-mixed gases. For example, in pro-mixed gaseous fuels on extremely low turn down the flame will backfire or blow off. With this construction the burners may operate without air being supplied through the ports BI. Because a thorough intermixing of the air and gas is assured in this construction these burners are highly efficient.

The above construction provides a furnace that may operate satisfactorily at any temperature from 300 degrees Fahrenheit to 24:00 degrees Fahrenheit. This construction permits of rapid heating from relatively low temperatures to relatively high temperatures and permits the return of the temperature in the furnace to relatively low temperatures from relatively high temperatures very quickly. Due to the staggering "the furnace.

7 of the burners, the turbulence of the productsof combustion and the flame and the cylindrical shape of the chamber 1 I, all'parts of the chamber are uniformly heated. The above features also insure that if the temperature of the chamber 1 l is changed, the temperature changes uniformly throughout the chamber. Due to the heating characteristics of this furnace; that is, wide temperature range and quick change to any preselected temperature, this furnace may be used for all phases of the hardening operation, in-

cluding pre-heating, hardening and tempering. Thus, this construction provides a single furnace that may be used to heat treat either carbon steels or high alloy steels. By providing for readyremoval and insertion of the cover 56 for the hearth this furnace can be readily changed from a seini-muiile to a full muffle furnace. This is advantageous not only because it permits the furnace to be cleaned readily but also because In furnace, the combination of a horizontally 1 disposed sleeve having horizontally disposed passageways in the Walls of the sleeve at staggered positions on opposite sides of the sleeve adjacent the bottom thereof in communication with the interior of the sleeve, end portions at opposite ends ofsaid sleeve-to define with said sleeve a horizontally disposed chamber having a door at one end'thereof, an article supporting hearth dis- "posed in said chamber, means for supporting said hearth to space the latter from the bottom of the chamber above the passageways including means acting between the hearth and said end portions, an upper muffle portion slidably supported on said hearth and removable through said door, where- 'by the furnace may be readily converted from a mufile furnace to a semi-mufile furnace, and gas burners associated with each passageway to discharge the products of combustion into said chamber to cause the latter to follow the curvature of the chamber and swirl about the interior thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,247,863 Nettgens Nov. 27, 1917 1,402,325 Vollkommer Jan. 3, 1922 r 1,517,172 Rudd NOV. 25, 1924 1,552,83 Fitch Sept. 8, 1925 1,710,870 Forse Apr. 30, 1929 2,075,694 Bonner et a1. Mar. 30, 1937 2,277,595 Levy et al Mar. 24, 1942 2,375,771 Dany et al. May 15, 1945 OTHER REFERENCES Pages 338 and 339 of Trinks Industrial Furnace, vol. II, 2nd edition, copyright 19%2, published by John Wiley & Sons, New York, New York. 

